Rate of strength increase of unsaturated lateritic soil

Lateritic soil is a kind of residual soil that is widely distributed in Asia. The water table of the soil is normally very deep so the upper part of the soil is often unsaturated. The largest lateritic soil area in Taiwan is the Linkou terrace. Because the soil here is loosely cohered and consolidated, the problem of slope instability and landslides has always been a major concern. To evaluate the triggering mechanism of landslides, it is necessary to obtain the failure criterion that represents both the saturated and unsaturated conditions of the soil before any analysis is carried out. The parameter required to define such a failure criterion is the rate of shear strength increase, tan φ b , which can be obtained via a series of laboratory strength tests in a modified triaxial system under various matric suction levels. Both the intact and remolded lateritic soils taken from Linkou terrace have been tested for this purpose. The results confirm that matric suction in the lateritic soil contributes significantly to the soil shear strength and that intact soil has a higher strength than remolded soil.